The Rev. Pat Robertson, the religious talk show host, today upstaged a parade of prospective 1988 Republican presidential candidates with a rousing speech accusing the Democratic Party chairman of bigotry against Christian fundamentalists.

On a day when potential candidates from Senate Majority Leader Robert J. Dole (R-Kan.) to former Delaware governor Pierre S. du Pont IV appealed for support from 2,000 southern Republicans gathered at a leadership conference here, Robertson brought sustained applause when he challenged Democratic National Committee Chairman Paul G. Kirk Jr. to a televised debate over a controversial Democratic fund-raising letter attacking Robertson by name.

"I found your letter to be so full of bigotry and so contrary to the basic American spirit of tolerance and fair play that I feel impressed to call for an apology," Robertson said, reading from a letter he sent to Kirk today.

Kirk's letter cited statistics showing a massive shift to the GOP among white evangelical Christians and warned that "with his massive financial resources and political organization and a mobile right-wing voting block behind him, Pat Robertson could well take the Republican nomination and be a candidate to be reckoned with in the general election."

In his letter, which raised little money for the party, Kirk contended that "Pat Robertson wants to abolish public education . . . , require that at least 25 percent of all government civil service employes be born-again Christians and launch a massive military buildup far larger than the Reagan administration's."

Robertson said the claims are untrue.

Responding to Robertson's challenge, Democratic National Committee spokesman Terry Michael said, "The letter addresses Pat Robertson's right-wing political agenda, not his religious views or those of any American . . . . If Pat Robertson is going to enter the political arena, he should develop a little thicker skin and not try to shield his radical political views by portraying them as religious beliefs."

Republican Party leaders today heard from a variety of prospective candidates who tried to distinguish themselves from each other while remaining generally uncritical of the Reagan administration.

One exception was former secretary of state Alexander M. Haig Jr., who contended that President Reagan's high-profile advocacy of his Strategic Defense Initiative (SDI), a missile defense system often known as "Star Wars," unnecessarily politicized the issue and gave the Soviets a bargaining demand in current arms negotiations.

Haig, a prospective 1988 candidate, also was the only speaker to take some light-hearted jabs at the president. Noting Reagan's need for a good night's rest, Haig said he was always encouraged when the president told him, " 'I'll have to sleep on that' because I knew that progress would begin immediately."

Rep. Jack Kemp (R-N.Y.) presented himself as someone who has the potential to attract blacks and blue-collar voters to the Republican Party. He said it is essential for the party to reach out to convert the "fragile" Reagan coalition "into a permanent partisan realignment." Kemp said black voters have greater opportunities in "the party of Lincoln, not the party of welfare."

Earlier, Tennesse Gov. Lamar Alexander (R) indirectly criticized Kemp by faulting Republican candidates who place excessive emphasis on such issues as a return to the gold standard while neglecting things such as education, highways and garbage collection.

Kemp countered that a return to the gold standard would force down interest rates to the 5 percent range, which "should be good for any Republican to run on."

Du Pont and Dole were well-received here today. Dole continued to advocate a constitutional amendment to balance the budget, while du Pont argued that the basic principles of the free market should guide the continued expansion of the conservative program launched by Reagan. Du Pont said this approach is valid not only in the economic arena but for arms control and education policy.

Expanding on this theme, du Pont contended that the SDI program will change the arms control "marketplace" by forcing the Soviets "to deal" and that the Reagan administration's proposed program of education vouchers would force increased marketplace competition among schools to produce quality education.